The present invention relates to a cutting tooth of a cutting device made from a thermoplastic material, wherein the cutting device can be operatively connected to a closure device that is attachable to a container covering and can be rotated about a rotational axis and wherein the cutting tooth is equipped with a tooth tip in a direction pointing away from an edge of the cutting device; thus enabling the cutting device to be used for opening the container covering for the first time.
Closure devices on containers made of plastic for storing free-flowing substances have been industrially manufactured in large numbers for a long time. The closure devices have a cutting device comprising at least one cutting tooth, the cutting device being operatively connected to the closure device. By manipulating a cap which is attachable to a pouring neck, both parts being part of the closure device, the cutting device is employed to open the container covering. The cutting device is rotated during the initial opening and moved linearly in the direction of the container covering; thus enabling the cutting teeth to cut open the container covering and provide an opening.
In order to achieve an opening of the container covering in a reproducible manner even when plastic layers and laminated layers consisting of plastic materials, light metal alloys and cardboard are used, the industry made due in recent years with a temporary solution. The container covering was equipped with a film patch which can easily be cut and into which the cutting teeth of the cutting device can easily cut.
After a first cutting tooth has pierced the container covering, said container covering is cut open or more precisely ripped open in the direction of rotation by said first cutting tooth or further cutting teeth equipped with a cutting edge.
All components of the closure device are as a rule produced or injection molded from thermoplastic materials as one piece in a plastic injection molding process. By simply pushing the components in the longitudinal direction of the axis of rotation of the closure device, the finished closure device which can be mounted to the container covering is assembled.
The cutting devices are injection molded using a central mold core and a mold encasing the mold core. The cavity between mold core and mold is correspondingly used to produce the cutting device. As a rule, the recess for the cutting tooth to be produced is either formed into the mold or the mold core, whereby a fast and simple parting of the two mold parts is facilitated. The parting plane or line between the two mold parts therefore aligns either with the outer surface of the mold core or the inner surface of the mold.
The cutting tooth was created with a maximally tapering tooth tip, whereby the parting line is disposed directly at the thinnest point of the tooth tip in an extending manner. Due to the geometry of the tip, a weakened tooth tip was achieved, which is flexible on account of the thin material layer as is known from the prior art and is depicted in FIG. 6.
Beside a weakly designed tooth tip due to small material thickness, edges and flashes result in the region of the parting line. Increased internal pressure in the injection molding tool can exceed the closing force between mold core and mold, whereby the parting plane is severely stressed. The force on the injection molding tools or, respectively, the parting plane is indicated with arrows in FIG. 6. A so-called breathing of the injection molding tool can occur and a portion of the injection mold material undesirably enters the region of the parting line between the two injection molding tool parts. An injection molding edge results in the region of the parting line and thereby on the outermost tooth tip. Said injection molding edge leads to an additional instability of the tooth tip. Such a tooth tip is not sufficiently tight and, depending on the container covering that is used and is to be pierced, does not have or has only a weak perforating effect and thus leads to a bending of the tooth.
Because a multiplicity of cutting teeth is used, one could have assumed that a sufficient perforating effect could nevertheless have been achieved and the container covering was at least partially pierced. As soon as the cutting teeth pierced the container covering, only the cutting effect of the cutting teeth was utilized, which is independent of the shape of the unstable tooth tip. In order to improve the cutting effect, the person skilled in the art has tried to develop suitable cutting teeth through the use of dimensionally stable plastics.
In order to solve this problem, the receptacle was manufactured from a high-strength plastic foil and a hole was punched out and was closed with a thinner film that can be perforated more easily. The closure device was subsequently welded thereupon. This process is time consuming and expensive.
The analyzed cutting results from known cutting devises reveal very ragged even sheered cutting lines. In order to pour the contents of a container out of closure device in a desirable manner, an improved and smooth cutting line that is as even as possible is desired, wherein it must be ensured in any case that no container covering material is separated and enters into the container or, respectively, the contents.